1. Field of the Invention
The present invention relates to a resin for toner of electrophotography, a method for manufacturing the same and a toner composition containing such a resin, and more specifically to a resin for toner which shows high humidity resistance and is stable to humidity.
2. Prior Art
Electrophotography is a technique for obtaining images by forming an electric latent image on a light-sensitive material according to various means utilizing a photoconductive substance, developing such an image with a toner, optionally transferring the toner image to a support for image such as paper and then fixing the image by means of, for instance, a heating roll to thus obtain an electrophotograph. Various kinds of resins have been developed to use them in such toners to be employed in electrophotography. Among these, polyester resins have presently been used widely as resins for toners which are fixed with a heating roll becuase they show good wettability to transfer paper and can disperse uniformly, therein, additives for toner such as carbon black when they are melted by applying heat and further, they can impart excellent fixing properties to the resulting toner (e.g. U.S. patent application No. 110,695 based on PCT JP87/00064, Jap. Pat. Kokai Koho Nos. 60-263950, 61-86760 and 62-70860).
In the electrophotography, it is always required to provide clear and stable images from the viewpoint of sending information.
However, in the conventional toners, the polyester resins used therein have, at their ends, hydrophilic groups such as carboxyl groups and hydroxyl groups derived from monomers constituting the polymers and, therefore, flow properties and shelf stability as well as charging properties of the toners are greatly influenced by change in environmental conditions, in particular, change in humidity. This makes it impossible to always obtain clear images according to electrophotography technique. As means for solving this problem, there has been proposed, for instance, a method for eliminating influences by such change in properties of the toners which comprises adding, to such a toner composition, additives such as fine powders of hydrophobic silica. This method can improve the properties of the toner in some degree, but is accompanied by a new problem that the surface of a light-sensitive material for copying apparatuses is impaired. Therefore, the foregoing problem has not yet been solved thoroughly.